Getting all you need

Setting up a Build Environment

Make sure that no interfering build environment (such as MSYS) is in your PATH environment variable when building.

Optional: Set Up Visual Studio

If you want to use Visual Studio to compile ReactOS, you need to get one of the supported version, which is VS2010 and later. You can download the free Community Edition of Visual Studio 2015. To compile with VS, open the appropriate VS command prompt and follow the same instructions as for building with the GCC based ReactOS build environment. Note that you still need the ReactOS build environment, which contains CMake and some additional tools, or you can install the latest version of CMake yourself, but that is not recommended. If you experience problems with the configure stage, e.g. the compiler is reported to not be working, please check if you have installed any additional Windows SDKs or WDK and try again after removing them.

Getting a Working Copy

The first step in building ReactOS is getting a copy of the source code.

You can use the exported release source code, but since you are reading this, you are probably interested in keeping up to date with the latest changes, so you will want a "working copy" of ReactOS.
To get a working copy of ReactOS, please read the ReactOS Git For Dummies page.

Prerequisites

Notice: It is recommended to temporarily disable your antivirus before proceeding, because some of them detect some of ReactOS' system files (in particular, crtdll.dll) as being infected.

Before building either the tools or ReactOS itself the output location must be created and prepared. This is an easy step and involves only one command. This command is located in the root of recent revisions of the source code and can be run either from the root directory itself or any other directory you want the build your sources in. Please make sure you are running it from within ReactOS BE:

Linux/Unix

Run:

configure.sh
cd output-MinGW-i386/reactos

Windows or ReactOS

Run:

configure.cmd
cd output-MinGW-i386

After executing, folder output-MinGW-i386 will be created in root of ReactOS tree. You will be redirected to it.
If you want to build in a different folder, cd to that folder first and then execute

<path_to_source>\configure.cmd

configure.cmd currently supports the following options:

/? displays help

Codeblocks creates a CodeBlocks solution

Eclipse creates an Eclipse solution

Makefiles creates (n)make files

clang Uses clang instead of gcc

VSSolution Creates a Visual Studio solution

RTC enables extra runtime checks

You can additionally specify any number of cmake command line options, like "-DSYMBOL=VALUE".

Building ReactOS on Windows or ReactOS*

From the build folder (e.g. reactos\output-MinGW-i386) enter the following command:

ninja COMMANDS

Replace "COMMANDS" with the desired build commands, such as bootcd or livecd, listed below:

* Perhaps, some functions of RosBE may not work on ReactOS. If so, please have a look on our Jira page whether this problem is already reported or not.

Building ReactOS on Unix/Linux

ninja COMMANDS

Combining the above steps together:
Replace "COMMANDS" with the desired build commands, such as bootcd or livecd, listed below:

Commands

After you have started a Build Environment Command Prompt, there are certain commands available.

Invoking a build

ninja or ninja all

This command builds all binaries of ReactOS. They will be placed in the created output directory created by the configure command. (default: output-MinGW-i386/reactos)
All source files, which did not change since the last build, will not be built again.

ninja bootcd

This command works like make, but also generates a bootable ReactOS ISO file (bootcd.iso) placed into the output directory.
It is wise to tag your Boot-CDs with the revision they were built from if you need to keep many ReactOS ISOs.

ninja livecd

This command generates livecd.iso in the output directory. This is the ReactOS Live-CD that runs completely from the CD-ROM.

ninja hybridcd

This command generates hybridcd.iso in the output directotry. This is a hybrid cd of ReactOS

Adding modules to the build process

There are several modules you can add to the build process. For example rosapps contains some additional applications not included by default.

The page Building Modules describes, which modules exist and how to add them to the build process.